Process for the disproportionation of alkylated aromatic primary amines

ABSTRACT

Alkylated aromatic primary amines undergo disproportionation and transalkylation in the presence of a catalyst comprising activated carbon or unmodified graphite and a Group VIIIA metal at a temperature between 200° C. and 500° C. Suitable Group VIIIA metals are selected from the group consisting of platinum, palladium, nickel, cobalt or mixtures thereof.

This application is a continuation-in-part of application Ser. No.913,826, filed on Sept. 30, 1986 now U.S. Pat. No. 4,801,951.

TECHNICAL FIELD

The present invention relates to disproportionation and transalkylationreactions of alkylated aromatic primary amines.

BACKGROUND OF THE INVENTION

Meta-phenylenediamine, a useful chemical intermediate, has been preparedby the catalytic reduction of m-dinitrobenzene. Dinitration of benzeneis difficult because the ring is deactivated and product separation isdifficult, thus rendering the dinitrobenzene feedstock form-phenylenediamine (M-PDA) synthesis very expensive. U.S. Pat. No.4,387,247 discloses the reduction of di- or polynitro aromatic compoundsby gaseous H₂ S over a solid catalyst. CO gas is added to promoteformation of amino groups from all nitro groups in the molecule. Thedisproportionation of toluenediamine (TDA) to m-PDA was reported as asecondary reaction under the CO/H₂ S atmosphere.

U.S. Pat. No. 4,405,812 discloses a process for the ortho dealkylationof aromatic amines by contacting o-methyl substituted aromatic amineswith a nickel catalyst at about 200°-400° C. The demethylation ofdimethylanilines over nickel catalysts resulted in poor selectivity tothe dealkylation product, toluidine when run under conditions similar tothose used in aromatic hydrocarbon disproportionation.

U.S. Pat. No. 3,123,644 discloses a process for dealkylating a nuclearpolyalkyl primary aromatic amine having a tertiary alkyl group of 4 or 5carbon atoms on at least one ring carbon atom in the ortho-position withrespect to the amino group. The polyalkyl primary aromatic amine isconverted into a mono-nuclear aromatic amine by heating at a temperaturein the range of 150°-350° C. under superatmospheric pressure with anacceptor aromatic amine and in the presence of a finely dividedsilica-alumina type catalyst.

U.K. patent application No. 810,751 discloses a process for thedealkylation of aromatic hydrocarbons. The process is carried out at atemperature from 450° to 700° C. and H₂ pressure above 40 atmospheres inthe presence of a catalyst comprising active carbon by itself or with asmall amount of metallic activator.

The chemistry of carbon is not well defined in regard to role as acatalyst or catalyst support. Kirk, R. E., Encyclopedia of ChemicalTechnology. Vol. 2, pp. 881-899, discloses on page 885 that activecarbon may be used as a catalyst in various reactions. In some instancesit is used alone, for example, to catalyze the formation of sulfurylchloride. However, more often it is used as a carrier for othercatalysts.

For example, U.S. Pat. No. 4,331,557 discloses a process forregenerating ruthenium containing catalysts suitable for hydrogenation,dehydrogenation, isomerization disproportionation, and hydrocrackingreactions. The reference states at col. 2, lines 16-29 that suchruthenium-containing catalysts may be supported on carbon, Kieselguhr,silica, alumina, silica-alumina, calcium carbonate, barium carbonate,pumice, clays and the like.

BRIEF SUMMARY OF THE INVENTION

The present invention is a process for the disproportionation andtransalkylation of alkylated aromatic primary amines wherein an aromaticprimary amine is contacted with a catalyst comprising activated carbonor unmodified graphite and a Group VIIIA metal at a temperature between200° C. and 500° C. Group VIIIA metals suitable for practicing thisinvention include platinum, palladium, nickel, cobalt and mixturesthereof. The same catalysts and reaction conditions can be used for thetransalkylation of two or more primary aromatic amines. Both thedisproportionation and transalkylation reactions are useful methods ofsynthesizing m-phenylenediamine.

The process may be carried out in the liquid phase at autogenouspressure. Preferably the process is carried out under an inertatmosphere. The present process is capable of selectively producingdesired disproportionation products while limiting secondary productformation, e.g. formation of deaminated and/or coupled products. Forexample, catalysts with high hydrogenation activity and acidic supports,such as Ni/Al₂ O₃, show high disproportionation activity but poorselectivity due to deamination and to reduction of aromatic rings.Additionally, the present process uses a preferred feedstock compared toprocesses involving the dinitration of benzene.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is a process for the disproportionation andtransalkylation of alkylated aromatic primary amines. An alkylatedaromatic primary amine is contacted with a catalyst comprising activatedcarbon or unmodified graphite and a Group VIIIA metal at temperaturesranging typically from about 200° C. to about 500° C. Catalysts suitablefor practicing the invention typically contain between 0.01%-10% by wt.of a Group VIIIA metal such as platinum, palladium, nickel, cobalt andmixtures thereof. Examples of the latter include 5% platinum on carbon,5% palladium on carbon, 5% nickel on carbon, platinum intercalatedgraphite, palladium intercalated graphite, Co intercalated graphite,carbons impregnated with up to 10% of a Group VIIIA metal reduced in H₂prior to use, etc.

While the above catalysts may be obtained from a variety of sources, theactivated carbon may conveniently be produced from the pyrolysis ofcoal, vegetables, wood, coconut, or oil. Alternatively, the activatedcarbon may be produced by the pyrolysis of a carbon-containingsubstrate, for instance a hydrocarbon on an oxide support such asalumina.

The reaction is preferably carried out at a temperature between 300° C.and 400° C. with a range of 200° C. to 500° C. being acceptable. Atlower temperatures the reaction rate is too slow to be practical and athigher temperatures deamination and coupled product formation occur.Reaction time will vary with the selected process conditions, with apreferred reaction time being that which is sufficient to give between20% to 35% conversion. At lower conversions, product isolation costs areincreased and at higher conversions, formation of secondary productsoccurs.

The reaction can be carried out via a variety of operating modes such asin a batch slurry reactor, e.g., a sealed stirred autoclave, atautogenous pressure, or by use of a CSTR or a trickle bed system with orwithout diluent gases. Other process steps can be taken to improve thereaction, such as recycling of heavy products through a flow reactor toreduce the rate of their formation, or separating products from thebatch reactor by continuous distillation. Preferably the reaction iscarried out under an inert atmosphere or a slight partial pressure of H₂(10-200 psi). Under high H₂ pressures (200-300 psi), or in the presenceof steam, higher yields of heavy products are produced. Suitablereaction atmospheres include: low pressures of H₂ (e.g.. about 10 psi);CO; ppm levels of H₂ S in an inert atmosphere; and ppm levels of H₂ S ina H₂ atmosphere.

Any suitable alkylated aromatic primary amine can be used as a reactantfor the disproportionation reaction, example including: 2,4Toluenediamine (TDA); 2,6 TDA; 2.3 TDA; 3,4 TDA; o-,m-,p-toluidines;alkyl substituted anilines alkyl substituted aromatic diamines,toluidines, etc. Representative disproportionation reactions using theabove reactants include;

    2,4TDA→m-phenylenediamine+xylenediamine (XDA)

    2,6TDA→m-phenylenediamine+xylenediamine

    Mixtures of 2,4 and 2,6 TDA→m-phenylenediamine+xylenediamine

    p-toluidine→aniline+xylidine.

The choice of reactants will depend upon the desired product. Sincem-phenylenediamine (m-PDA) is a highly valued chemical intermediate fora variety of applications, reactants such as 2,4 TDA or 2,6 TDA whichdisproportionate to yield m-PDA are often the preferred reactants.Optionally, the primary amines employed in the reaction can be formed insitu from secondary or tertiary amines used as the starting material.

In addition to disproportionation reactions, the catalysts and processconditions of the present invention are also suitable fortransalkylation reactions. Transalkylation results when an alkylatedaromatic primary amine is reacted with a second aromatic compound.Transalkylation proceeds by the same mechanism and under the sameconditions as the disproportionation described above, with the onlydifference being that the alkyl groups are transferred between aromaticcompounds having different structures. Representative examples of suchtransalkylation reactions include:

    TDA+aniline→m-PDA+toluidine

    XDA+aniline→TDA+toluidine

    XDA+cumene→benzene+isopropyl XDA

It is believed that aromatic amine disproportionation and/ortransalkylation occurs either by an acid catalyzed or a free radicalmechanism, and the reaction will also occur slowly in the absence ofcatalyst due to thermal homolytic cleavage and radical formation.Activated carbons are known to contain high concentrations of unpairedelectrons and are catalytic for disproportionation probably because theycan abstract hydrogen from TDA, forming the benzyl radicals which areintermediates in disproportionation by a radical mechanism. Further, theactivated carbons are unable to hold the hydrogen in a labile enoughstate to cause cleavage of the bonds of the intermediates to enableproduct formation. The ability of the catalyst to activate hydrogen isstill low enough that H₂ in the headspace is not activated for ringhydrogenation. As a result, hydrogenated rings, which are intermediatesin the formation of heavy products, are not formed, and alsohydrodeamination does not occur. Another possible explanation for thecatalytic behavior of these carbon-containing catalysts may lie in theirweak acidity. Carbons contain oxygenated functions which may be strongenough acids to catalyze disproportionation of TDA, but weak enough thatheavy products are not formed.

Catalysts with high hydrogenation activity and acidic supports, such asNi/Al₂ O₃ have previously shown high disproportionation activity, butpoor selectivity due to deamination and to the reduction of rings. Theseproblems are avoided with carbon-containing catalysts of the presentinvention. In the prior art when TDA was selectively disproportionatedover Ni/Al₂ O₃, this was under a CO/H₂ S atmosphere and thedisproportionation was probably selective because the atmospherepoisoned the ring hydrogenation activity of the Ni. Such an atmosphereis not necessary with the carbon catalysts.

Several examples were carried out in accordance with the process of thepresent invention. These examples are described below and are only meantto illustrate the invention and are not meant to be limiting.

EXAMPLE 1

A 300 cc stirred autoclave was charged with 50 g of 2,4 toluenediamineand 2.00 g NUCHAR® C-190N activated charcoal available commercially fromWestvaco. The reactor was purged with He, sealed under 1 atmosphere He,heated to 350° C. over approximately 20 minutes, stirred at 700 RPM, andmaintained at 350° C. for 4 h. The reactor was cooled to 80° C., asample dissolved in methanol, the catalyst separated by sedimentationand the methanol soluble product analyzed for aromatic compounds by gaschromatography, using an internal standard to obtain a mass balance.

The composition of the product is given in Table 1 below. Conversion ofTDA was 25.9% with 47.9% selectivity to m-phenylenediamine, which is95.8% selectivity for disproportionation.

Selectivities (SEL) are calculated as follows: ##EQU1##

EXAMPLE 2

An identical test to Example 1 above was carried out for 16 h.Conversion of TDA was 41.7% with 45.8% selectivity to m-phenylenediamineand a disproportionation is selectivity of 87.8%. The productselectivity is set out in Table 1 below.

EXAMPLE 3

The procedure set out in Example 1 above was carried out using 2,6 TDAas the reactant. Conversion of TDA was 25% with 33.9% selectivity tom-phenylenediamine and a disproportionation selectivity of 59.6%. Theproduct selectivity is set out in Table 1.

EXAMPLE 4

This example demonstrates the utility of the present invention for acommercial mixture of 2,4 TDA and 2,6 TDA (80:20 mixture). An autoclave,charged with 40.0 g of 2,4 TDA. 10.0 g of 2,6 TDA and 2.00 g of NUCHAR®carbon, was set up, operated and sampled at 4 h as in Example 1. Theproduct selectivity is given in Table 1.

EXAMPLE 5

A catalyst was prepared by the following procedure:

A solution of 4.45 g of Ni(CH₃ COO)₂ ·4H₂ O in 100 ml anhydrous methanolwas added to 20.0 g NUCHAR® C-190N carbon with constant stirring, afterwhich the methanol was evaporated over a steam bath while stirring. Theproduct was reduced at 400° C. under 1 atm H₂ for 20 h in a flowreactor, then transferred in air to the slurry reactor.

The catalyst was tested by the procedure described in Example 2 using2.0 g of catalyst and 50 g of 2,4 TDA Product selectivity is shown inTable 1.

EXAMPLE 6

The procedure of Example 2 above was carried out using 2.0 g ofEngelhardt 5.0% Pt on carbon (Engelhardt lot 26505) as the catalyst, and50 g of 2,4 TDA as the reactant. The product selectivity is given inTable 1.

EXAMPLE 7

Example 6 was repeated, with Engelhardt 5.0% Pd on carbon (Engelhardtlot 26885) employed as the catalyst in place of 5.0% Pt on carbon. Theproduct selectivity of this run is also shown in Table 1 below.

                                      TABLE 1                                     __________________________________________________________________________    Catalyst Performance Data for the Disproportionation of TDA                                   Selectivities                    Dispropor-                                   m-phenylene-                                                                         Diamino-       Diamino-    tionation                   Example                                                                            Catalyst                                                                           TDA Conv                                                                            diamine                                                                              xylene                                                                             Toluidine                                                                          Xylidine                                                                           mesitylene                                                                          Heavies                                                                            Selectivity                  __________________________________________________________________________    1    Nuchar                                                                             25.9  47.9   47.9 0    0    0.66   3.51                                                                              95.8                         2    Nuchar                                                                             41.7  45.8   42.0 0.11 0.08 1.17  10.80                                                                              87.8                         3    Nuchar                                                                             25.0  33.9   25.7 0.28 0.21 1.07  38.9 59.6                         4    Nuchar                                                                             38.2  31.5   29.2 0    0    0.75  38.5 60.7                         5    Ni/C 48.7  34.7   33.0 0    0    0.86  31.5 67.7                         6    Pt/C 57.2  35.7   34.8 0.2  0    1.28  22.3  70.52                       7    Pd/C 49.4  43.0   42.4 0.3  0    1.59  12.7 85.4                         __________________________________________________________________________

EXAMPLE 8

While Examples 1-7 above all use diamines as the reactant, the presentprocess can also be carried out using primary alkylated aromaticmonoamines. To demonstrate this, the procedure detailed in Example 1above was carried out using 50 g p-toluidine as starting materialinstead of 2,4-TDA. Product analysis by gas chromatography is given inTable 2 below.

                  TABLE 2                                                         ______________________________________                                        Disproportionation of p-toluidine using Carbon Catalyst Example 8             Selectivities                                                                 Conv    m-toluidine                                                                              Aniline   Xylidine                                                                              Heavies                                  ______________________________________                                        12.8    8.8        34.5      30.7    26.0                                     ______________________________________                                    

EXAMPLE 9

Six runs were carried out using the process conditions and procedures ofExample 1 for the disproportionation of TDA. Runs 1-5 employed thecarbon-containing catalysts of the present invention, and Run 6 was acomparative run using Ni/Al₂ O₃ catalyst which was employed in thereactions of U.S. Pat. No. 4,405,812. The Pt/C catalyst of run 2 wasreduced with hydrogen prior to the reaction.

The results of all six runs as reported in Table 3 below.

                  TABLE 3                                                         ______________________________________                                        Catalyst Performance Data for the Disproportionation of TDA                                Selectivities                                                    Run  Catalyst  Conv.   M-PDA   XDA   Tol. Heavies                             ______________________________________                                        1    Nuchar C  42      45      42    0    11                                  2    Pt/C.sup.1                                                                              44      49      46    0     3                                  3    Pt/C      57      35      34    0    22                                  4    Ni/C      49      35      33    0    31                                  5    Pd/C      49      43      42    0    13                                  6    Ni/Al.sub.2 O.sub.3                                                                     74      22      12    15   40                                  ______________________________________                                         .sup.1 Prereduced in H.sub.2, Tol. = toluidine, mPDA =                        metaphenylenediamine, XDA = xylenediamine                                

The results shown in Table 3 above indicate that the prior art Ni/Al₂ O₃catalyst results in products that are formed by the polymerization ofTDA or the products as well as the deamination product, toluidine.Consequently, although high conversions are achieved with the Ni/Al₂ O₃catalyst, it is not suitable for the present invention. The carbon-basedcatalysts of the present invention are thermodynamically limited to alower conversion, but produce significantly less unwanted high molecularweight products, and are therefore well suited for the production ofm-PDA and similar products.

Additionally, as can be seen by comparing runs 2 and 3, treating thePt/C catalyst with H₂ prior to reaction with the TDA results insignificant selectivity improvements.

Having thus described the present invention, what is now deemedappropriate for Letter Patent is set out in the following appendedclaims.

What is claimed is:
 1. A process for the disproportionation of alkylatedaromatic primary amines which comprises contacting said alkylatedaromatic primary amines with a catalyst comprising activated carbon orunmodified graphite and a Group VIIIA metal at a temperature between200° C. and 500° C.
 2. The process in accordance with claim 1 whereinsaid Group VIIIA metal is selected from the group consisting ofplatinum, palladium, nickel, cobalt and mixtures thereof.
 3. The processin accordance with claim 2 wherein said alkylated aromatic primary amineis a diamine.
 4. The process in accordance with claim 3 wherein saiddisproportionation results in the production of m-phenylenediamine. 5.The process in accordance with claim 4 wherein said alkylated aromaticprimary amine is toluenediamine.
 6. The process in accordance with claim1 wherein said alkylated aromatic primary amine is contacted with saidcatalyst at a temperature between 300° C. and 400° C.
 7. The process inaccordance with claim 1 wherein said disproportionation is carried outunder autogenous pressure.
 8. The process in accordance with claim 1wherein said disproportionation is carried out in the presence of aninert blanket gas.
 9. The process in accordance with claim 1 whereinsaid alkylated aromatic primary amine is toluidine.
 10. The process inaccordance with claim 1 wherein said disproportionation produces anilineand xylidine.
 11. The process in accordance with claim 1 wherein saiddisproportionation is carried out in a batch slurry reactor in theliquid phase.
 12. The process in accordance with claim 1 wherein saiddisproportionation is carried out in a continuous flow reactor.
 13. Theprocess in accordance with claim 1 wherein said catalyst is an activatedcarbon produced from the pyrolysis of coal, vegetables, wood, coconut oroil.
 14. The process in accordance with claim 1 wherein said carboncontaining catalyst is treated with H₂ prior to being contacted with thereactants.
 15. The process in accordance with claim 1 wherein theselectivity for disproportionation products is greater than 95%.
 16. Aprocess for the transalkylation of two or more aromatic primary amines,wherein at least one aromatic amine is an alkylated aromatic amine, saidprocess which comprises contacting said aromatc primary amine with acatalyst comprising activated carbon or unmodified graphite and a GroupVIIIA metal at a temperature between 200° C. and 500° C.
 17. The processin accordance with claim 16 wherein one of the primary aromatic aminesis selected from the group consisting of toluenediamine, xylenediamineand aniline.
 18. The process in accordance with claim 16 wherein saidtransalkylation results in the production of m-phenylenediamine.
 19. Theprocess in accordance with claim 16 wherein said transalkylation iscarried out in a temperature between 300° C. and 400° C.
 20. The processin accordance with claim 16 wherein said carboncontaining catalyst istreated with H₂ prior to being contacted with the aromatic primaryamines.